Optical discs, such as compact discs (CD) and digital versatile discs (DVD) are a form of computer readable media which provide extensive storage for digital information. While some optical discs may be read-only, others may additionally be written-to. Typically, one side of the disc is referred to as the data side and the other side of the optical disc is referred to as the label side. The label side may include factory-prepared label text and graphics.
An optical disc drive (ODD) of a computer is used to read from, and in certain cases to write to, the data side of an optical disc. An optical pickup unit (OPU), included within the optical disc drive, is configured with a laser and sensors adapted for reading, and possibly writing, data. Various ODDs and OPUs are available, and are manufactured to specifically read and write to the data side of optical discs.
Using emerging technology, the OPU assembly may be is used to define an image on the label surface of an optical disc configured for such a labeling process. However, during the labeling process conventional focusing systems used within the OPU assembly will not work properly. A number of reasons exist for this failure. First, known OPU assemblies in ODDs are designed to focus light through a layer of clear polycarbonate, onto a data track defined on top of the layer. As a result, the optics in known OPUs are designed to compensate for refraction resulting from light passage through the polycarbonate. In contrast, when marking the label surface, light must be focused directly onto the top of the label surface, and does not pass through any layer of transparent material. Accordingly, the corrections built into the optics which cancel the refraction resulting from light travel through the polycarbonate present a problem when attempting to focus existing OPUs on a label surface.
A second reason for the difficulty encountered in focusing light on the label surface of a disc is that conventional OPUs, which are configured to focus light through the polycarbonate, are effectively designed to focus light at a distance which is greater than the distance to the surface of the disc. Accordingly, to focus on the surface of the disc, signals sent to the optics must be reconfigured to focus at the surface of the disc, rather than at a more distant location, such as the data track within the disc.
A third reason for the difficulty encountered in focusing light on the label surface of the disc is that conventional OPUs are configured to focus on data pits defining a data track, which is typically backed by a reflective covering of aluminum. This reflective covering provides a very smooth and uniformly reflective surface, which reflect laser light uniformly. Sensors which detect the reflected light tend to have a very high signal-to-noise ratio. In contrast, light is not uniformly reflected off the label surface of the disc, and the sensors which detect this reflected light have a very low signal-to-noise ratio.
Accordingly, the need exists for new and improved systems and methods to control focal optics within optical disc drives.